Use of annular flumes to determine the influence of current velocity and bivalves on material flux at the sediment-water interface

A benthic annular flume for both laboratory and in situ deployment on intertidal mudflats is described. The flume provides a means of quantifying material flux (i.e., biodeposition of suspended particulates, sediment resuspension, nutrients, oxygen, and contaminants) across the sediment-water interface in relation to changes in current velocity and benthic community structure and/or population density of key macrofauna species. Flume experiments have investigated the impact of the infaunal bivalve Macoma balthica and the epifaunal bivalve Mytilus edulis on seston and sediment flux at the sediment-water interface. The bioturbator Macoma was found to increase die sediment resuspension and/or erodability by 4-fold, at densities similar to those recorded at the Skeffling mudflat (Humber estuary) (i.e., >1000 individuals m(-2)). There was a significant correlation between sediment resuspension and Macoma density (r = 0.99; p < 0.001), which supported previous in situ field observations indicating bioturbation by Macoma enhanced sediment erodability. Biodeposition rates (g m(-2) h(1)) of Mytilus edulis and Cerastoderma edule were quantified and related to changes in population density in a mussel bed (Cleethorpes, Humber estuary). Biodeposition rates were up to 40-times the natural sedimentation rates. At the highest mussel bed densities (i.e., 50-100% cover or >1400 mussels m(2)) the physical presence of this epifaunal bivalve on the sediment surface reduced erosion by 10-fold. The shift from net biodeposition to net erosion occurred at current velocities of 20-25 cm s(-1). These results demonstrate that infaunal and epifaunal bivalves can have a significant impact on seston flux or sediment deposition and on sediment resuspension or erodability in estuaries where there are extensive mudflats.